This application relates to a patterned electromagnetic interference shielding coating applied to the exterior surface of a protective optical element. The coating consists of an electromagnetic interference shielding feature which is placed in channels in a substrate surface, and which is typically formed of a semiconductor.
Transparent protective optical elements are utilized in a number of applications. One application is to protect an image capturing device. The image capturing device may be a camera associated with an aircraft such as a surveillance vehicle. The surveillance vehicle may attempt to capture images over a wide spectrum of wavelengths. Another application is to protect a beam delivery device such as a laser communication system or a laser targeting system.
It is important to shield or block electromagnetic interference (EMI) from harming the electronics contained within such systems.
Three ways of blocking the EMI are known.
In the first, the material chosen for the substrate is conductive and therefore will itself block EMI. Such substrates typically do not transmit visible radiation and therefore are limited to infrared applications.
A second method is to provide a grid of metal as a coating on the exterior surface of the substrate. Because of the voids present in the grid metal, these coatings are transparent to light of any wavelength out to long-wavelength infrared, and therefore as prior art are preferred for applications requiring the widest range of wavelength band transmission.
In a third method, an electrically conductive coating is placed on the outer surface of the substrate and is formed of a semiconductor material that is relatively transparent to visible and near-infrared light. However, the semiconductor coating transparency is zero at potentially critical longer wavelengths.
In wavelengths that cannot be transmitted through the coating, there is no ability to capture any image.
It has been proposed to embed metal mesh within a surface of the substrate. This does not address the concerns mentioned above.